Title

Author

Publication Date

Spring 2018

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Advisor

Robert B. Miller

Subject Areas

Geology

Abstract

The 48 Ma Golden Horn batholith is a ~310 km2, shallow intrusion constructed of sub-horizontal sheets in the crystalline core of the North Cascades of Washington. It is the only large body of granite in an orogen dominated by 96-45 Ma tonalite, and probably intruded during ridge subduction. The oldest and structurally highest unit of the batholith is diorite, followed by alkaline granite, one feldspar-biotite granite, two feldspar-biotite granite, and finally granodiorite, the youngest and structurally lowest unit. The batholith displays a weak NE-striking foliation restricted to the center of the intrusion and a stronger NW-striking foliation formed throughout the batholith with an associated weak, NW-trending and shallowly plunging lineation. Foliation is coupled across the northwestern and parts of the southern contact, and likely records a NE-SW shortening component in an overall transtensional regime. Most Golden Horn dikes intruding host rock are felsic, but there are some mafic dikes. These steeply dipping dikes tend to form swarms and strike NE and E-W. The NE-striking dikes reflect regional NW-SE extension. Parts of the southern contact are marked by xenolith-rich zones, which are ~100 m wide and several km long, and lend evidence to stoping as an emplacement mechanism. The diking, stoped blocks, and lack of a ductile aureole are compatible with shallow batholith emplacement models.